Rapid prototyping describes various techniques for fabricating a three-dimensional prototype of an object from a computer model of the object. One technique is three-dimensional printing whereby a special printer is used to fabricate the prototype from a plurality of two-dimensional layers. In particular, a digital representation of a 3-D object is stored in a computer memory. Computer software sections the representation of the object into a plurality of distinct 2-D layers. A 3-D printer then fabricates a layer of material for each layer sectioned by the software. Together, the various fabricated layers form the desired prototype.
In one method of three-dimensional printing, layers of a powder material are deposited in a confined area. A binder solution is selectively deposited on each layer to produce regions of bound powder. The unbound powder is then removed to yield a three-dimensional part.
In accordance with the invention, a three-dimensional printer fabricates a three-dimensional object from a digital representation stored in memory. In a particular embodiment, the digital representation is provided from memory by a computer. One or more mechanisms may be employed with the printer to enhance or improve the quality of the fabricated object.
In particular, a work area of the printer includes a feed reservoir, a build table, an overflow cavity and a fabrication assembly. Build material is stored in the feed reservoir in a powdered form and is extracted as required to build the three-dimensional object. The build table receives an incremental deposit of build powder transferred from the feed reservoir. The build powder can reacts with an applicable binder to form a solid region. Excess build powder which is not deposited on the build table can be received at the overflow cavity. During fabrication, airborne build material can be created in the work area. A flow of air across each layer of build powder during printing reduces the drying time for the binder to improve the print quality.
In a particular embodiment, a filtration system, which may include a vacuum pump and a filter, can be coupled to the overflow cavity to remove excess build powder from the overflow cavity. The filtration system can also include a dehumidifying element to remove excess moisture from the air. The filtration system can draw air from the overflow cavity during operation of the printer. The user can select to divert the suction to an inlet to act as a moveable, miniature vacuum cleaner.
The filtration system can recirculate the filtered, dehumidified air from the work area to a clean area of the printer. The clean area can include electronics and other equipment damageable by the airborne build material. A partial seal can be employed to separate the work area from the clean area and a mechanical coupling can extend through the partial seal to operate the fabrication assembly. A positive pressure differential helps to keep airborne powder out of the clean area.
Binder liquid can be applied by a moveable gantry suspended over the feed reservoir, the build table and the overflow cavity. The gantry can also include a spreader for transferring build material from the feed reservoir to the build table to create incremental layers. The gantry includes binder jets in at least one binder cartridge, each binder jet being coupled to a supply of binder to selectively deposit binder on the layers of build material. In a particular embodiment, the binder cartridges are operated with pressure-controlled binder solution.
Varied volumes of binder can be applied to selected positions in the layers of build material. By applying these varying quantities of binder, the strength of the part can be controlled. In particular, a greater volume of binder is deposited at the perimeter of the cross-section to create a hard outer shell or in the interior of the cross-section to create a truss or other support structure. Varying volumes can be deposited by varying the flow rate of the binder from the jets or by depositing binder a variable number of times at a selected position.
The binder can include color dyes. Drops of binder and dyes can be selectively deposited on a layer of build material to create a multi-colored object. In particular, the dyes can be selectively deposited to color the outside surface of the object. The binder itself can be uncolored or combined with the dyes.
During operation, the binder jets can be clogged by debris, including a mixture of the binder and the build material. A cleaning assembly on the gantry can include a wiper membrane to remove build material and other debris from the binder jets. In particular, a wiper element is provided in a path from the binder jets. The binder jets are periodically directed to travel across the wiper element so the wiper element can dislodge residue from the jets. The wiper element can be cleaned by flowing binder material from the jets over the wiper element to clean the wiper element. The resulting waste liquid can be collected for disposal in a waste container.
For a number of reasons, including clogging and misalignment, a particular binder jet in a print cartridge may become faulty. The faulty jet can create an undesired line of delamination in each layer of build material. To address this problem, the binder jets can be offset by a fixed distance between successive layers. This offsetting creates a discontinuity between the lines of delamination. This shingling effect is created by laterally offsetting the binder jets relative to the direction of a print scan.
Any of a number of post-processing mechanisms or techniques may be used to improve the quality of the fabricated objected. These can include infiltration and coatings.
The feed reservoir and the build chamber are piston chambers or boxes, which can be fabricated from a unitary material. The piston boxes include sides which join each adjacent side at a curved interior comer. A piston is chosen to have a shape which compliments the interior shape of the box. A seal is provided between the outside edges of the piston and the interior surface of the box to retain the build material over the pistons. The box can be formed by shaping a flexible metal belt to form a smooth interior surface. The curved interior comers are formed by wrapping the belt around a plurality of rods to define the comers. The belt is then fixed in place by a volume of curable urethane and, after curing, the rods are removed to yield a piston box having a smooth interior surface.
The above and other features including various novel details of construction and combination of parts, will be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and apparatus for prototyping a three-dimensional object embodying the invention is shown by illustration only and not as a limitation of the invention. The principal and features of this invention may be embodied in varied and numerous embodiments without departing from the scope of the invention.